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init: Add option to listen on sockets before starting service.

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Review note: Original change was a p-o-c by agl in
https://r.android.com/2094350 which I think is actually
production quality.  I'm just taking it over so that he doesn't
get spammed by any review comments as that's not a good use
of his time.

Needed for the hardware entropy daemon (see bug).

Original commit message:
If one needs to create a service that synchronously starts listening on
a socket then there are currently no good options.

The traditional UNIX solution is to have the service create the socket
and then daemonise. In this situation, init could start the service with
`exec_start` and yet not block forever because the service forks and
exits. However, when the initial child process exits, init kills the
daemon process:

> init: Killed 1 additional processes from a oneshot process group for
> service 'foo'. This is new behavior, previously child processes
> would not be killed in this case.

Next, there is a `socket` option for services and (although the
documentation didn't nail this down), the socket is created
synchronously by `start`. However, init doesn't call `listen` on the
socket so, until the service starts listening on the socket itself,
clients will get ECONNREFUSED.

This this change adds a `+listen` option, similar to `+passcred` which
allows a socket service to reliably handle connections.

Bug: 243933553
Test: Started prng_seeder from init using the new listen flag
Change-Id: I91b3b2b1fd38cc3d96e19e92b76c8e95788191d5
This commit is contained in:
Adam Langley 2022-05-11 22:32:47 +00:00 committed by Pete Bentley
parent 633ce78b94
commit ecc14a5958
7 changed files with 22 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
init/README.md
View file

@ -352,9 +352,10 @@ runs the service.
`socket <name> <type> <perm> [ <user> [ <group> [ <seclabel> ] ] ]`
> Create a UNIX domain socket named /dev/socket/_name_ and pass its fd to the
launched process. _type_ must be "dgram", "stream" or "seqpacket". _type_
may end with "+passcred" to enable SO_PASSCRED on the socket. User and
group default to 0. 'seclabel' is the SELinux security context for the
launched process. The socket is created synchronously when the service starts.
_type_ must be "dgram", "stream" or "seqpacket". _type_ may end with "+passcred"
to enable SO_PASSCRED on the socket or "+listen" to synchronously make it a listening socket.
User and group default to 0. 'seclabel' is the SELinux security context for the
socket. It defaults to the service security context, as specified by
seclabel or computed based on the service executable file security context.
For native executables see libcutils android\_get\_control\_socket().

3
init/property_service.cpp
View file

@ -1404,7 +1404,8 @@ void StartPropertyService(int* epoll_socket) {
StartSendingMessages();
if (auto result = CreateSocket(PROP_SERVICE_NAME, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK,
false, 0666, 0, 0, {});
/*passcred=*/false, /*should_listen=*/false, 0666, /*uid=*/0,
/*gid=*/0, /*socketcon=*/{});
result.ok()) {
property_set_fd = *result;
} else {

9
init/service_parser.cpp
View file

@ -434,11 +434,14 @@ Result<void> ServiceParser::ParseSocket(std::vector<std::string>&& args) {
<< "' instead.";
}
if (types.size() > 1) {
if (types.size() == 2 && types[1] == "passcred") {
for (size_t i = 1; i < types.size(); i++) {
if (types[i] == "passcred") {
socket.passcred = true;
} else if (types[i] == "listen") {
socket.listen = true;
} else {
return Error() << "Only 'passcred' may be used to modify the socket type";
return Error() << "Unknown socket type decoration '" << types[i]
<< "'. Known values are ['passcred', 'listen']";
}
}

3
init/service_utils.cpp
View file

@ -168,7 +168,8 @@ void Descriptor::Publish() const {
Result<Descriptor> SocketDescriptor::Create(const std::string& global_context) const {
const auto& socket_context = context.empty() ? global_context : context;
auto result = CreateSocket(name, type | SOCK_CLOEXEC, passcred, perm, uid, gid, socket_context);
auto result = CreateSocket(name, type | SOCK_CLOEXEC, passcred, listen, perm, uid, gid,
socket_context);
if (!result.ok()) {
return result.error();
}

1
init/service_utils.h
View file

@ -54,6 +54,7 @@ struct SocketDescriptor {
int perm = 0;
std::string context;
bool passcred = false;
bool listen = false;
bool persist = false;
// Create() creates the named unix domain socket in /dev/socket and returns a Descriptor object.

7
init/util.cpp
View file

@ -89,8 +89,8 @@ Result<uid_t> DecodeUid(const std::string& name) {
* daemon. We communicate the file descriptor's value via the environment
* variable ANDROID_SOCKET_ENV_PREFIX<name> ("ANDROID_SOCKET_foo").
*/
Result<int> CreateSocket(const std::string& name, int type, bool passcred, mode_t perm, uid_t uid,
gid_t gid, const std::string& socketcon) {
Result<int> CreateSocket(const std::string& name, int type, bool passcred, bool should_listen,
mode_t perm, uid_t uid, gid_t gid, const std::string& socketcon) {
if (!socketcon.empty()) {
if (setsockcreatecon(socketcon.c_str()) == -1) {
return ErrnoError() << "setsockcreatecon(\"" << socketcon << "\") failed";
@ -145,6 +145,9 @@ Result<int> CreateSocket(const std::string& name, int type, bool passcred, mode_
if (fchmodat(AT_FDCWD, addr.sun_path, perm, AT_SYMLINK_NOFOLLOW)) {
return ErrnoError() << "Failed to fchmodat socket '" << addr.sun_path << "'";
}
if (should_listen && listen(fd, /* use OS maximum */ 1 << 30)) {
return ErrnoError() << "Failed to listen on socket '" << addr.sun_path << "'";
}
LOG(INFO) << "Created socket '" << addr.sun_path << "'"
<< ", mode " << std::oct << perm << std::dec

4
init/util.h
View file

@ -44,8 +44,8 @@ static const char kColdBootDoneProp[] = "ro.cold_boot_done";
extern void (*trigger_shutdown)(const std::string& command);
Result<int> CreateSocket(const std::string& name, int type, bool passcred, mode_t perm, uid_t uid,
gid_t gid, const std::string& socketcon);
Result<int> CreateSocket(const std::string& name, int type, bool passcred, bool should_listen,
mode_t perm, uid_t uid, gid_t gid, const std::string& socketcon);
Result<std::string> ReadFile(const std::string& path);
Result<void> WriteFile(const std::string& path, const std::string& content);